Bad Air Days in Weber County, Utah: 11 a Year

11 bad air days a year

Among the worst tenth of monitored US counties. Ranked 80 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (33% particle days).

The bad-air season here

Most bad days here fall in July and August and February. Averaged over 2016 to 2025.

Is a purifier worth it here?

Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.
Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.

The worst days on file

In 2000 to 2009 this county averaged 26 bad days a year; in 2016 to 2025, 11. The air has improved. The worst recent year was 2017, with 23 bad days on 365 monitored days.

Date	AQI	Main pollutant
2017-07-04	166	PM2.5
2018-07-04	159	PM2.5
2017-02-02	153	PM2.5
2018-08-11	151	Ozone
2016-08-02	143	Ozone

The air on a normal day

Across 3,595 monitored days from 2016 to 2025, the air in Weber County rated Good on 60% of them, less often than the 72% typical of monitored counties, and Moderate on 38%. The median day sat at AQI 47; one day in ten went above 79.

The pollutant setting the AQI on an ordinary day here:

ozone67%2,421 days
fine particles (PM2.5)25%916 days
nitrogen dioxide6%215 days
coarse dust (PM10)1%40 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	240	123	2	0	45	119
2024	366	243	117	6	0	45	122
2023	365	218	141	6	0	47	141
2022	365	205	155	5	0	48	121
2021	364	221	126	17	0	46	140
2020	366	228	132	6	0	45	140
2019	308	224	82	2	0	44	108
2018	365	181	167	17	2	51	159
2017	365	175	167	23	2	51	166
2016	366	207	139	20	0	49	143
2015	365	197	155	13	1	50	189
2014	365	172	184	9	2	52	180
2013	365	106	219	40	5	57	166
2012	366	139	205	22	1	54	167
2011	365	172	171	22	4	51	160
2010	365	134	207	24	2	54	165

*2025 may be a partial year in EPA's file.

Elsewhere in Utah

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.